Rear-wheel suspension for two-wheeled vehicle

ABSTRACT

A rear-wheel suspension system for a two-wheeled vehicle capable of further reducing a vehicle width. An upper end of a coil spring of a shock absorber includes a tubular damper case, a rod connected to a piston disposed within the shock absorber and protrusively provided to be capable of making strokes with respect to the tubular damper case and an external hydraulic sub-tank positioned to be lower than an upper end of the shock absorber. Vehicle body component parts include a connecting tube and the sub-tank disposed to be close to the shock absorber above the coil spring.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 USC 119 to JapanesePatent Application No. 2006-024335 filed on Feb. 1, 2006 the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rear-wheel suspension system for atwo-wheeled vehicle.

2. Description of Background Art

A rear-wheel suspension system for a two-wheeled vehicle is knownwherein a swing arm is provided with a front portion that is pivotallysupported by a vehicle body frame and extends rearwardly from a headpipe. A rear portion supports a rear wheel. A shock absorber is providedthat is disposed such that its longitudinal direction coincides with avertical direction. An upper portion of the shock absorber is pivotallysupported between center frames and a rear portion is pivotallysupported by the swing arm,

The related-art shock absorber is disposed such that a buffer ispositioned above the shock absorber and a coil spring is positioned in astate that is close thereto. A vehicle body component part such as anoutlet case is placed at a lateral position of the coil spring. See, forexample, JP-Y No. 2522667 (Page 2, FIG. 2).

Thus, in the related-art rear-wheel suspension system for a two-wheeledvehicle, the buffer and the coil spring are disposed to be close to eachother. The close arrangement requires a space corresponding to the outerdiameter of the spring. In addition, the vehicle body component partsuch as the outlet case is disposed at a lateral position of the coilspring, which imposes a limitation on the dimensions of the system.

SUMMARY AND OBJECTS OF THE INVENTION

Therefore, the present invention has been developed in consideration ofsuch a situation, and it is an object of an embodiment of the presentinvention to provide a rear-wheel suspension system for a two-wheeledvehicle, capable of further deducing the vehicle width.

For achieving this object according to an embodiment of the presentinvention, a rear-wheel suspension system for a two-wheeled vehicleaccording to the present invention employs the following technicalmeasures.

More specifically, a rear-wheel suspension system for a two-wheeledvehicle according to an embodiment of the present invention includes apair of right- and left-side center frames connected to a rear portionof a main frame extending rearwardly from a head pipe and extendingdownwardly. A swing arm includes a front portion which is pivotallysupported by the center frames and a rear portion for supporting a rearwheel. A shock absorber, disposed such that its longitudinal directioncoincides with a vertical direction, includes an upper portion which ispivotally supported on a vehicle body side between the center frames. Alower portion of the shock absorber is pivotally supported on the swingarm side. The shock absorber includes a tubular buffer and a springdisposed around the buffer with an upper end of the spring beingpositioned to be lower than an upper end of the buffer. A vehicle bodycomponent part is placed to be close to the buffer above the spring.

In the rear-wheel suspension system for a two-wheeled vehicle accordingto an embodiment of the present invention, the vehicle body componentpart is an intake-system part for making a connection between an enginedisposed in front of the buffer and an air cleaner disposed to the rearof the buffer.

In the rear-wheel suspension system for a two-wheeled vehicle accordingto an embodiment of the present invention, the vehicle body componentpart is a sub-tank which is a component part of the buffer.

A rear-wheel suspension system for a two-wheeled vehicle according to anembodiment of the present invention includes a pair of right- andleft-side center frames connected to a rear portion of a main frameextending rearwardly and downwardly from a head pipe. A swing armincludes a front portion which is pivotally supported by the centerframes and a rear portion which is made to support a rear wheel. A shockabsorber, disposed such that its longitudinal direction coincides with avertical direction, is provided with an upper portion which is pivotallysupported on a vehicle body side between the center frames and a lowerportion which is pivotally supported on the swing arm side. The shockabsorber includes a buffer with a tubular cylinder and a spring disposedaround the buffer. An upper end of the spring is positioned to be lowerthan an upper end of the cylinder and a sub-tank is integrally formed ina state that is close to the cylinder above the spring so as to combinea portion of a wall surface constituting the cylinder and a portion of awall surface constituting the sub-tank.

According to an embodiment of the present invention, a bufferconstituting a shock absorber is disposed on an upper side. A ring-likemounting position of a coil spring is placed on an lower side with avehicle body component part being disposed to be brought close to orabut on the buffer above the coil spring. This enables the vehicle bodycomponent part to be shifted toward the interior side of the vehiclebody by a dimension corresponding to the coil spring. Thus, a reductionin the dimensions of the width of the vehicle are obtained.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a side-elevational view showing a two-wheeled vehicle having arear-wheel suspension system for a two-wheeled vehicle according to anembodiment of the invention;

FIG. 2 is an enlarged side-elevational view showing an essential part ofthe present invention in FIG. 1;

FIG. 3 is a plan view simply showing a center frame and peripheralportions as the essential part of the present invention;

FIG. 4 is a front-elevational view simply showing a shock absorber andperipheral portions as the essential part of the present invention; and

FIG. 5 is a vertical cross-sectional view showing a shock absorber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will be given of an embodiment of a rear-wheel suspensionsystem for a two-wheeled vehicle according to the present invention. Asan example, the rear-wheel suspension system for a two-wheeled vehicleaccording to the present invention is applied to an off-road two-wheeledvehicle including a four-cycle single-cylinder engine. A detaileddescription will be omitted except a construction section of arear-wheel suspension system which forms an essential part.

As shown in FIG. 1, the basic construction of a motorcycle according tothis embodiment includes a front suspension 2 for pivotally supporting afront wheel 1. A head pipe 3 is provided for pivotally supporting thefront suspension 2. A main frame 4 extending with two-branchesrearwardly from the head pipe 3. A pair of right-side and left-sidecenter frames 5 are connected to a rear portion of the main frame 4 andextend downwardly. A down frame 6 and lower frame 7 are joined so as toconnect lower portions of the center frames 5 and the head pipe 3. Apower unit 8 includes a four-cycle single-cylinder engine. A seat rail10 extends to above a rear wheel 9 attached to the center frames 5. Ahandlebar 11 is connected to the front suspension 2. A swing arm 12includes a front portion pivotally supported by the center frames 5 anda rear portion for supporting the rear wheel 9. A sprocket 91 and chain13 transmit the driving force of the power unit 8 to the rear wheel 9. Ashock absorber 14, disposed such that its longitudinal directioncoincides with a vertical direction, includes an upper portion pivotallysupported between the center frames 5 and a lower portion rotationallysupported through a link mechanism. A front fender 15 is positioned tocover the front wheel 1 with a rear fender 15 being positioned to coverthe rear wheel 9. A seat 17 is set on the seat rail 10 with a fuel tank18 located at an upper portion of a front side of the vehicle body. Thetwo-wheeled vehicle may be operated by a handlebar and by use of athrottle and other controls operated by a rider sitting on the seat 17.

The above-mentioned power unit 8 includes a four-cycle single-cylinderengine 81 located in a region defined by the main frame 4, the centerframes 5, the down frame 6 and the lower frame 7. A throttle body 82 isattached to an intake side of the engine 81 with an air cleaner 83, aconnecting tube (intake system part) 84 for making a connection betweenthe throttle body 82 and the air cleaner 83 and a muffler 86 equippedwith an exhaust pipe 85 secured to the exhaust side of the engine 81.

The rear-wheel suspension according to an embodiment of the presentinvention is used with the above-mentioned construction of themotorcycle having the center frames 5, the swing arm 12, the shockabsorber 14 and the connecting tuber 84 (intake system part).

The center frames 5 are a pair of right-side and left-side frames eachof which is connected to rear portions of the main frame 4 extending ina two-branch fashion rearwardly from the head pipe 3. As shown in FIG.2, a cross pipe 19 is laid to make a connection between upper parts ofthe center frames 5. Moreover, in the vicinity of the cross pipe 19 forthe center frames 5, cushion blankets 20, each having a bearing portion20 a made therein, extend to confront each other toward their insides.

The swing arm 12 is shaped into a plan-viewed gate configuration so thata front portion thereof is pivotally supported by lower portions of thecenter frames 5 to be swingable in vertical directions. The rear wheel 9is rotatably supported by a rear portion of the swing arm 12. At aportion under the front side of the swing arm 12, a first pivotallysupporting portion 21 a of a first link member 21 includes a generallytriangular configuration, provided in confronting relation thereto, thatis pivotally supported. A second pivotally supporting portion 21 b isformed at a lower position than the first pivotally supporting section21 a and is pivotally engaged with a bar-like second link member 22pivotally supported by a fourth pivotally supporting portion 22 aprovided in the center frames 5 at a lower position than a pivotallysupporting portion between the center frames 5 and the swing arm 12. Inaddition, a third pivotally supporting portion 21 c is positioned infront of the first link member 21 with the generally triangularconfiguration being pivotally supported by the tip of a rod 14 b.

As shown in FIGS. 2 and 5, the shock absorber (buffer) 14 is a so-calledshock absorber having a tubular damper case 14 a internally including acylinder 14 g. The rod 14 b is connected to a piston 14 h protrusivelypositioned in the interior of the damper case 14 a to be capable ofmaking strokes with respect to the damper case 14 a. An externalhydraulic sub-tank 14 c (vehicle body component part), with a coilspring 14 d is circularly mounted so as to extend over the rod 14 b andthe damper case 14 a.

In addition, in comparison with a related-art shock absorber, in thecase of this shock absorber 14, the position of the coil spring 14 d isshifted further downwardly. In addition, the sub-tank 14 c (vehicle bodycomponent part) and the damper case 14 a are integrated through a wallsurface 14 m, combining them, to form a housing so that they are placedside by side in a vehicle width direction. The cylinder 14 gcommunicates through a damping force control valve 14 k with theinterior of the sub-tank 14 c.

As shown in FIG. 5, the center line of the sub-tank 14 c is not inparallel with the center lines of the damper case 14 a, the rod 14 b andothers, and a lower portion of the sub-tank 14 c is slightly inclinedoutwardly to make a required angle θ (preferably, approximately 2°),which improves the workability of the sub-tank 14 c.

In the shock absorber 14 thus constructed, a first fitting portion 14 elying on an upper side of the damper case 14 a is pivotally supportedbetween the bearing portions 20 a of the shock absorber brackets 20formed protrusively to confront the insides of the center frames 5. Asecond fitting portion 14 f is provided on a tip portion of the rod 14 band is pivotally supported by the third pivotally supporting portion 21c of the first link member 21 provided at a lower portion near the frontside of the swing arm 12. As shown in FIGS. 1 to 3, the damper case 14 ais fitted to be slightly inclined in the forward direction and islocated at a generally central position in the vehicle width direction.

In this embodiment, the shock absorber 14 and the swing arm 12 areconnected to each other through the first link member 21 and the secondlink member 22, thereby varying the stroke amount of the rod 14 b withrespect to the swinging angle of the rear wheel 9. More specifically,although a sufficient shock absorber characteristic is obtainable whenthe rear wheel 9 is deeply lowered, there is no restriction on this.However, it is also appropriate that the shock absorber 14 and the swingarm 12 are directly connected to each other.

As shown in FIGS. 1 and 2, the connecting tube 84 (intake system part)is a curved tubular member for making a connection between the throttlebody 82 placed in front of the shock absorber 14 and the air cleaner 83placed in the rear of the shock absorber 14. As shown in FIGS. 3 and 4,the connecting tube 84 is disposed to be close to the damper case 14 aso as to detour from the opposite side to the sub-tank 14 c.

The connecting tube 84 and the sub-tank 14 c are located at the rightand left sides, respectively, in a state wherein the damper case 14 a isinterposed therebetween. The muffler 86 is placed on the sub-tank 14 cside.

Since it is not easy to change the height layout of this connecting tube84 greatly from the viewpoint of the layout of the power unit 8, in astate where this height position is taken as an absolute position,according to this embodiment, the position of the coil spring 14 d isshifted downwardly so that the connecting tube 84 and the sub-tank 14 care moved toward the interior of the vehicle body by a dimensioncorresponding to the coil spring 14 d.

As described above, in the rear-wheel suspension system according tothis embodiment, the position of the coil spring 14 d is shifteddownwardly so as to move the vehicle body component parts such as theconnecting tube 84 and the sub-tank 14 c toward the interior of thevehicle body by a dimension corresponding to the coil spring 14 d, whichcan further reduce the width dimension of the vehicle body.

This reduction in the vehicle width improves the rider foot-landingcharacteristic and, with respect to the connecting tube 84, the detourfor preventing an interference with the shock absorber 14 is furtherreduced in comparison with the related-art shock absorber. Thus, furtherimprovements with respect to the intake efficiency are expected.

Although a rear-wheel suspension system for a two-wheeled vehicleaccording to this embodiment has been described above, theabove-described embodiment relates to one example of the best mode ofthe present invention, and the present invention is not limited to thisbut it is acceptable to cover all changes of the embodiment herein whichdo not constitute departures from the spirit and scope of the invention.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A rear-wheel suspension system for a two-wheeledvehicle comprising: a pair of right- and left-side center framesconnected to a rear portion of a main frame extending rearwardly anddownwardly from a head pipe; a swing arm having a front portionpivotally supported by the center frames and a rear portion forsupporting a rear wheel; and a shock absorber, wherein a longitudinaldirection of the shock absorber coincides with a vertical direction, theshock absorber having an upper portion pivotally supported on a vehiclebody side between the center frames and a lower portion pivotallysupported on the swing arm side; wherein the shock absorber includes atubular buffer and a spring disposed around the buffer with an upper endof the spring being positioned to be lower than an upper end of thebuffer and a vehicle body component part being placed at a lateral sideof the buffer, a bottom end of the vehicle body component being locatedabove the upper end of the spring and below the upper end of the buffer,wherein a center line of a sub-tank that is the vehicle body componentpart is non-parallel with a center line of a damper case of the buffer,and wherein the center line of the sub-tank is slightly inclinedoutwardly compared to the center line of the damper case of the buffer.2. The rear-wheel suspension system for a two-wheeled vehicle accordingto claim 1, further comprising an intake-system part for making aconnection between an engine disposed in front of the buffer and an aircleaner disposed in the rear of the buffer, wherein the intake-systempart is placed at the later side of the buffer, and a bottom end of theintake-system part is located above the upper end of the buffer.
 3. Therear-wheel suspension system for a two-wheeled vehicle according toclaim 1, wherein the sub-tank forms a component part of the buffer. 4.The rear-wheel suspension system for a two-wheeled vehicle according toclaim 1, wherein the tubular buffer includes a tubular damper case asthe damper case with a cylinder formed therein with a piston and apiston rod operatively movable within said cylinder, said piston rodprojecting outside the tubular damper case and being engaged at a distalend thereof with said spring.
 5. The rear-wheel suspension system for atwo-wheeled vehicle according to claim 4, wherein said tubular bufferhas a predetermined length with a spring engaging portion being formedat a position displaced from said upper end of said tubular buffer andsaid tubular buffer extending downwardly from said spring engagingportion for enabling said piston and said piston rod to be movablewithin said cylinder in a range above and below said spring engagingportion.
 6. The rear-wheel suspension system for a two-wheeled vehicleaccording to claim 4, and further including a sub-tank operativelyconnected to said tubular buffer with a damping force control valvebeing in communication with said cylinder and said sub-tank forproviding communication therebetween.
 7. The rear-wheel suspensionsystem for a two-wheeled vehicle according to claim 6, wherein saidsub-tank and said tubular buffer are integrally formed with a commonwall divided therebetween, a first lateral wall surface of the commonwall constituting a portion of an inner surface the cylinder, a secondlateral wall surface of the common wall constituting a portion of aninner surface the sub-tank, the second lateral wall surface of thecommon wall being opposite to the first lateral wall surface of thecommon wall.
 8. The rear-wheel suspension system for a two-wheeledvehicle according to claim 1, wherein a muffler is placed on the sameside as a sub-tank that is the vehicle body component part.
 9. Therear-wheel suspension system for a two-wheeled vehicle according toclaim 1, wherein the center line of the sub-tank and the center line ofthe damper case of the buffer both extend downwardly toward the rearwheel.
 10. A rear-wheel suspension system for a two-wheeled vehiclecomprising: a pair of right- and left-side center frames connected to arear portion of a main frame extending rearwardly and downwardly from ahead pipe; a swing arm having a front portion pivotally supported by thecenter frames and a rear portion for supporting a rear wheel; and ashock absorber, wherein a longitudinal direction of the shock absorbercoincides with a vertical direction, the shock absorber having an upperportion pivotally supported on a vehicle body side between the centerframes and a lower portion pivotally supported on the swing arm side;wherein the shock absorber includes a buffer with a tubular cylinder anda spring disposed around the buffer, and an upper end of the spring ispositioned to be lower than an upper end of the cylinder, and a sub-tankis integrally formed with the tubular cylinder above the spring, thesub-tank and the tubular cylinder being divided by a common wall, afirst lateral wall surface of the common wall constituting a portion ofan inner surface the cylinder, a second lateral wall surface of thecommon wall constituting a portion of an inner surface the sub-tank, thesecond lateral wall surface of the common wall being opposite to thefirst lateral wall surface of the common wall, wherein a center line ofthe sub-tank is non-parallel with a center line of a damper case of thebuffer, and wherein the center line of the sub-tank and the center lineof the damper case of the buffer both extend downwardly toward the rearwheel.
 11. The rear-wheel suspension system for a two-wheeled vehicleaccording to claim 10, wherein the cylinder includes a piston and apiston rod operatively movable within said cylinder, said piston rodprojecting outside the buffer and being engaged at a distal end thereofwith said spring.
 12. The rear-wheel suspension system for a two-wheeledvehicle according to claim 11, wherein said cylinder has a predeterminedlength with a spring engaging portion being formed at a positiondisplaced from said upper end of said cylinder and said tubular bufferextending downwardly from said spring engaging portion for enabling saidpiston and said piston rod to be movable within said cylinder in a rangeabove and below said spring engaging portion.
 13. The rear-wheelsuspension system for a two-wheeled vehicle according to claim 11, andfurther including a sub-tank operatively connected to said tubularbuffer with a damping force control valve being in communication withsaid cylinder and said sub-tank for providing communicationtherebetween.
 14. The rear-wheel suspension system for a two-wheeledvehicle according to claim 13, wherein said sub-tank and said cylinderare integrated relative to each other with the common wall formedtherebetween forming a substantially a figure eight in an outercircumference thereof.
 15. The rear-wheel suspension system for atwo-wheeled vehicle according to claim 10, wherein a muffler is placedon the same side as the sub-tank.
 16. The rear-wheel suspension systemfor a two-wheeled vehicle according to claim 10, wherein the center lineof the sub-tank is slightly inclined outwardly compared to the centerline of the damper case of the buffer.
 17. A rear-wheel suspensionsystem for use with a vehicle comprising: a swing arm having a frontportion pivotally supported by a vehicle body frame and a rear portionfor supporting a rear wheel; and a shock absorber having an upperportion pivotally supported on the vehicle body frame and a lowerportion pivotally supported on the swing arm; wherein the shock absorberincludes a tubular buffer and a spring disposed around the buffer withan upper end of the spring being positioned to be lower than an upperend of the buffer and a vehicle body component part being placed at alateral side of the buffer, a bottom end of the vehicle body componentbeing located above the upper end of the spring and below the upper endof the buffer, wherein a center line of a sub-tank that is the vehiclebody component part is non-parallel with a center line of a damper caseof the buffer, and wherein the center line of the sub-tank is slightlyinclined outwardly compared to the center line of the damper case of thebuffer.
 18. The rear-wheel suspension system for use with a vehicleaccording to claim 17, further comprising an intake-system part formaking a connection between an engine disposed in front of the bufferand an air cleaner disposed in the rear of the buffer, wherein theintake-system part is placed at the later side of the buffer, and abottom end of the intake-system part is located above the upper end ofthe buffer.
 19. The rear-wheel suspension system for use with a vehicleaccording to claim 17, wherein the sub-tank forms a component part ofthe buffer.
 20. The rear-wheel suspension system for use with a vehicleaccording to claim 17, wherein the tubular buffer includes a tubulardamper case as the damper case with a cylinder formed therein with apiston and a piston rod operatively movable within said cylinder, saidpiston rod projecting outside the tubular damper case and being engagedat a distal end thereof with said spring.
 21. The rear-wheel suspensionsystem for use with a vehicle according to claim 20, wherein saidtubular buffer has a predetermined length with a spring engaging portionbeing formed at a position displaced from said upper end of said tubularbuffer and said tubular buffer extending downwardly from said springengaging portion for enabling said piston and said piston rod to bemovable within said cylinder in a range above and below said springengaging portion.
 22. The rear-wheel suspension system for use with avehicle according to claim 20, and further including a sub-tankoperatively connected to said tubular buffer with a damping forcecontrol valve being in communication with said cylinder and saidsub-tank for providing communication therebetween.
 23. The rear-wheelsuspension system for use with a vehicle according to claim 22, whereinsaid sub-tank and said tubular buffer are integrally formed with acommon wall divided therebetween, a first lateral wall surface of thecommon wall constituting a portion of an inner surface the cylinder, asecond lateral wall surface of the common wall constituting a portion ofan inner surface the sub-tank, the second lateral wall surface of thecommon wall being opposite to the first lateral wall surface of thecommon wall.
 24. The rear-wheel suspension system for a two-wheeledvehicle according to claim 17, wherein a muffler is placed on the sameside as a sub-tank that is the vehicle body component part.
 25. Therear-wheel suspension system for a two-wheeled vehicle according toclaim 17, wherein the center line of the sub-tank and the center line ofthe damper case of the buffer both extend downwardly toward the rearwheel.
 26. A rear-wheel suspension system for a two-wheeled vehiclecomprising: a pair of right- and left-side center frames connected to arear portion of a main frame extending rearwardly and downwardly from ahead pipe; a swing arm having a front portion pivotally supported by thecenter frames and a rear portion for supporting a rear wheel; and ashock absorber, wherein a longitudinal direction of the shock absorbercoincides with a vertical direction, the shock absorber having an upperportion pivotally supported on a vehicle body side between the centerframes and a lower portion pivotally supported on the swing arm side;wherein the shock absorber includes a tubular buffer and a springdisposed around the buffer with an upper end of the spring beingpositioned to be lower than an upper end of the buffer and a vehiclebody component part being placed at a lateral side of the buffer, abottom end of the vehicle body component being located above the upperend of the spring and below the upper end of the buffer, and wherein aconnecting tube, which connects a throttle body placed in front of acushion unit and an air cleaner placed in rear of the cushion unit, anda sub-tank that is the vehicle body component part are located at theright side and the left side, respectively, in a state where a dampercase of the buffer is interposed therebetween, and the connecting tubeis located to be close to the buffer above the spring.
 27. A rear-wheelsuspension system for a two-wheeled vehicle comprising: a pair of right-and left-side center frames connected to a rear portion of a main frameextending rearwardly and downwardly from a head pipe; a swing arm havinga front portion pivotally supported by the center frames and a rearportion for supporting a rear wheel; and a shock absorber, wherein alongitudinal direction of the shock absorber coincides with a verticaldirection, the shock absorber having an upper portion pivotallysupported on a vehicle body side between the center frames and a lowerportion pivotally supported on the swing arm side; wherein the shockabsorber includes a buffer with a tubular cylinder and a spring disposedaround the buffer, and an upper end of the spring is positioned to belower than an upper end of the cylinder, and a sub-tank is integrallyformed with the tubular cylinder above the spring, the sub-tank and thetubular cylinder being divided by a common wall, a first lateral wallsurface of the common wall constituting a portion of an inner surfacethe cylinder, a second lateral wall surface of the common wallconstituting a portion of an inner surface the sub-tank, the secondlateral wall surface of the common wall being opposite to the firstlateral wall surface of the common wall, and wherein a connecting tube,which connects a throttle body placed in front of a cushion unit and anair cleaner placed in rear of the cushion unit, and the sub-tank arelocated at the right side and the left side, respectively, in a statewhere a damper case of the buffer is interposed therebetween, and theconnecting tube is located to be close to the buffer above the spring.28. A rear-wheel suspension system for use with a vehicle comprising: aswing arm having a front portion pivotally supported by a vehicle bodyframe and a rear portion for supporting a rear wheel; and a shockabsorber having an upper portion pivotally supported on the vehicle bodyframe and a lower portion pivotally supported on the swing arm; whereinthe shock absorber includes a tubular buffer and a spring disposedaround the buffer with an upper end of the spring being positioned to belower than an upper end of the buffer and a vehicle body component partbeing placed at a lateral side of the buffer, a bottom end of thevehicle body component being located above the upper end of the springand below the upper end of the buffer, and wherein a connecting tube,which connects a throttle body placed in front of a cushion unit and anair cleaner placed in rear of the cushion unit, and a sub-tank that isthe vehicle body component part are located at the right side and theleft side, respectively, in a state where a damper case of the buffer isinterposed therebetween, and the connecting tube is placed to be closeto the buffer above the spring.